Most prior art engine governors may be classified as either "all-speed" or "min-max" governors. The use of such prior art governors on, for example, diesel engines give inherently poor driveability and throttle feel. The all-speed governors tend to feel strong under light throttle accelerations, but the engine performance severely diminishes as engine speed increases. Min-max governors give increasing engine power as engine speed increases and tend to make the engine feel weak after a transmission shift. Furthermore, the problems of the prior art engine governors are exacerbated when the engines are coupled to automatic transmissions.
Typical constant throttle curves for a diesel internal combustion engine having an all-speed governor are illustrated in FIG. 1. On a typical acceleration from a stop, with an automatic transmission, the driver will typically push the throttle down, for example, about 25%. The driver will think that he or she has requested plenty of throttle because the engine fuel pump will immediately increase to full fuel in order to try to raise the engine speed. If the vehicle does not move, the engine output will drop to about 150 ft-lbs at 1200 r.p.m., as dictated by the torque converter absorption curve 10. As the vehicle starts to move, the engine speed will slowly creep toward 1500 r.p.m., but this may not be enough to convince the automatic transmission to shift to the next gear. Consequently, the driver may need to increase the throttle setting in order to get enough vehicle speed to make the next shift. Unfortunately, the automatic transmission takes this increased throttle position as a desire for a higher shift point and the shift will be even further delayed. When the transmission finally shifts, the engine torque dramatically increases as the speed drops and the stress on the transmission clutches is severe, particularly on the shift into lock-up, where there is no torque converter to soften the impact.
Similar problems exist with the use of a manual transmission, except that the problems mostly center around the ability to get the engine speed high enough at light throttle settings to be able to shift to the next gear. Coming advances in vehicles and transmissions (continuously variable transmissions (CVT), hydrostatic drives and Hybrid vehicles) will further challenge traditional throttle logic. Control systems will need to clearly understand the driver's requirements as the system is optimized for each operating condition.
Typical constant throttle curves for a diesel engine employing a min-max governor are illustrated in FIG. 2. The min-max governor gives basically constant engine torque for any given throttle setting, regardless of engine speed. The problem with this type of prior art governor is that engine output power increases linearly with speed at a constant torque output, so the driver of the vehicle often needs to decrease the throttle setting in order to control acceleration. This may cause a premature shift and the driver will have to increase the throttle setting again after the shift because the output power of the engine has dropped with the engine speed drop. This may then cause the transmission to downshift again, or at least upset the driver, due to the required constant changes in throttle position.
It will therefore be appreciated by those skilled in the art that prior art engine governors exhibit problems related to driveability, throttle feel, and selection of transmission shift points (particularly when used with an automatic transmission). There is therefore a need for a throttle progression control system which does not exhibit the problems with the prior art systems. The present invention is directed toward providing such a throttle progression control system.